When many balls are used while practicing tennis for training purposes, the process of retrieving or collecting the balls represents an interruption of the playing and training process which can be undesirable for many reasons. Especially when a ball throwing machine is used for the training of one or more tennis players, and the ball throwing machine throws out a number of balls in a short time, the process of retrieving the balls is very lengthy in proportion to the effective training time. This increases the relative expenditure for the training particularly when the ball throwing machine and/or the tennis court is rented out per time unit, particularly by the hour. From that point of view, the process of ball retrieval is undesirable, because it represents lost training time.
For that reason ball retrieval systems with a movable retrieving arm are already known, which are intended to simplify the retrieval or collection of the tennis balls. In a first known embodiment as disclosed by German Offenlegungsschrift 32 42 358, the retrieving arm extends in the starting position along the side of the tennis court and can be swiveled around approximately 90.degree. into a position extending along the rear edge of the court for retrieval and collection of the balls lying on the court. The basic drawback of this construction lies in that a swivelable retrieving arm cannot sweep over the entire surface of one half of a tennis court and also the border areas.
In another known retrieval system, as disclosed in U.S. Pat. No. 4,456,252 and U.S. Pat. No. 4,606,543, a retrieving arm is provided which extends parallel to the net, is approximately the same length as the net and can be moved for the retrieval and collection of the balls in longitudinal direction along the tennis court to its rear border. There the retrieving arm thrusts the balls onto a ball receiving channel extending along the tennis court rear border, which transports them by means of a conveyor belt or by dropping into a ball collection container.
The system of U.S. Pat. No. 4,456,262 suffers from the imperfection that the retrieving arm does not rest on the border of the tennis court during the training but rather rests on or at the net in the middle of the tennis court. That is irritating, because the players often run forward up to the net and then cannot concentrate solely on the ball, but rather must also pay attention that they do not run into the retrieving arm. Also, each operation of the retrieving arm requires considerable time, because it must be returned to its original position at the net following retrieval of the balls each time before the training can be resumed once again. During practice the retrieving arm cannot be moved at all, even when no person is found in the relevant half of the tennis court, because the retrieving arm of this arrangement and direction of movement is not in the position to convey the balls falling to the ground between said retrieving arm and the net into the ball receiving channel at the end of the tennis court. No ball receiving channel can be arranged under the net and also the balls thrust therein by the retrieving arm are gathered up only with difficulty.
As a retrieving arm which is movable lengthwise to the tennis court cannot remain at the net during training, in accordance with U.S. Pat. No. 4,606,543 the retrieving arm has its starting position at the top of the tennis court lying opposite the ball receiving channel and during the collection of the balls it must move back and forth over the entire length of the tennis court. The interruption of training for that purpose in this case lasts even as much as twice as long as with a system according to U.S. Pat. No. 4,456,252. Also the retrieving arm must be sufficiently short that it can pass through between the posts supporting the net, so that at the side edges of the tennis court tennis balls lying outside the posts cannot be collected.